1. Field of the Invention
This invention relates to a magnetic head for digital recording, and more particularly to a magnetic head in which the influence of the leakage flux during operation is minimized.
2. Description of the Prior Art
In digital recording on a magnetic tape, magnetic disc, magnetic drum, magnetic card reader or the like, the S/N ratio has heretofore been a critical factor which affects the reliability of the recording.
Particularly, in these devices which must have interchangeability of devices and replaceability of data, minimization of the influence of unerased old data or the influence of the data on an adjacent track (crosstalk) has been a fundamental and important problem for improving the S/N ratio and further the reliability.
To overcome such a problem, various systems have heretofore been employed as shown in FIGS. 1, 2 and 3 of the accompanying drawings. The method shown in FIG. 1 is one which utilizes a combination of an erase head and a read-and-write head and in which the read-and-write head 2 is disposed downstream of the erase head 1 with respect to the direction of tape movement, D. FIG. 2 shows a method which utilizes a combination of a write-in head and a read-out head and in which the read-out head 4 is disposed downstream of the write-in head 3 with respect to the direction of tape movement, D. FIG. 3 shows a method which employs a combination of a read-and-write head and a tunnel erase head and in which two erase heads 1 are disposed downstream of the read-and-write head 2 with respect to the direction of tape movement D so as to erase the opposite widthwise edge portions of the tape which have been recorded by the head 2.
These systems are highly effective to enhance the S/N ratio, but the presence of theoretically plural gaps has required division or combination of heads which in turn has left numerous points still to be improved for practical use, such as the complexity of construction, the difficulty with which the heads make intimate contact with the recording medium, the higher cost of the head unit, etc.
In an effort to eliminate such disadvantages and moreover, to attain a simplified construction and higher reliability, there has been proposed a magnetic head improved as shown in FIGS. 4 and 5. FIG. 4 is a perspective view showing the internal structure of such improved magnetic head and FIG. 5 is a pictorial perspective view thereof. In FIGS. 4 and 5, there is seen a write-in excitation core 5, a write-in excitation winding 13 coiled around the excitation core 5, a read-out core 6 having a narrower track width than that of the write-in excitation core 5 and disposed in opposed relationship with the core 5 to form a closed magnetic circuit with a gap 9 interposed between the cores 5 and 6, a read-out excitation winding 14 coiled around the read-out core 6, dummy cores 7 disposed adjacent to the read-out core 6 with a non-magnetic spacer 8 interposed between the read-out core 6 and the dummy cores 7 with respect to the widthwise direction of the read-out core track, so as to form a closed magnetic circuit with the write-in excitation core 5 and a gap 9 interposed between the dummy cores, a holder member 10 for holding said cores, external terminals 11 provided on the holder member 10, and an outer casing 12. All these members together constitute a magnetic head generally designated by 15.
The basic operation of the magnetic head will now be described by reference to FIGS. 6 and 7 which illustrate the operations of the magnetic head of FIGS. 4 and 5 during write-in and read-out, respectively. In FIG. 6, it will be seen that information may be recorded on a tape 16 over the entire width of the core 5 by a signal current flowing to the excitation coil 13. More specifically, the magnetic flux produced by the write-in excitation core 5 skips over the gap 9 to flow into the read-out core 6 and the dummy cores 7, but since all these cores with the write-in excitation core 5 constitute the closed magnetic circuit, magnetic recording is effected uniformly with respect to the widthwise direction of the track as indicated by slant lines (although, when the spacers are inserted, the portions of the tape occupied by them are difficult to magnetize, the effect of which will later be described).
Referring to FIG. 7 which illustrates the read-out operation, it will be seen that only if the read-out core 6 lies within the range of the write-in core 5, output is stable wherever the read-out core is situated. In other words, most of the magnetic flux resulting from the signal magnetization on the dummy cores 7 is short-circuited by the excitation (write-in) core 5 and dummy cores 7 while only very small part of the flux comes to leak to the core 6. Therefore, if such a small quantity of leakage is negligible, the shown magnetic head will be identical in operational principle to the system of FIG. 2 which employs a combination of a write-in head and a read-out head. Thus, in spite of being of a single gap construction, the present magnetic head 15 is one which may perform a wide write-in operation as indicated by the rightwardly downwardly inclined lines and a narrow read-out operation as indicated by leftwardly downwardly inclined lines.
As can be judged from the above-described basic operation, it is necessary in putting such magnetic head into practical use that the following two conflicting conditions be solved: that during write-in, uniform magnetization can be accomplished throughout the great width of the write-in core 5; and that during read-out, the magnetization on the dummy cores 7 should not leak to the read-out core 6. In other words, during write-in, the absence of the spacers 8 disposed between the read-out core 6 and the dummy cores 7 is desirable while, during read-out, the presence of such spacers is necessary to reduce the leakage. Therefore, when the magnetic head 15 is to be put into practice, determining the dimensions and configuration of the spacers 8 is an important problem and this is why such head has not been put into practice as yet.